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| United States Patent |
5,293,942
|
|
Gewanter
, et al.
|
March 15, 1994
|
Oil well acidizing with iron chelating derivatives of aldohexoses and
aldopentoses such as a salt or acid of 2-ketogluconate
Abstract
This invention relates to the use of certain keto and diketo acids, esters
and salts that are derived from aldopentoses and aldohexoses, to maintain
very high levels of iron in solution under oil well acidizing conditions.
The compounds described herein chelate ferric iron at low temperatures and
are activated by heat to reduce ferric iron to the more soluble ferrous
species at high temperatures. Because of these properties and their
extraordinarily high solubility in hydrochloric acid, such compounds are
capable of maintaining considerably more iron in solution than competing
materials.
| Inventors:
|
Gewanter; Herman L. (Waterford, CT);
Graham; Sandra I. (Mystic, CT);
Rashan, Jr.; Joseph M. (Waterford, CT);
Reitz; R. Larry (Salem, CT)
|
| Assignee:
|
Pfizer Inc. (New York, NY)
|
| Appl. No.:
|
840375 |
| Filed:
|
February 24, 1992 |
| Current U.S. Class: |
166/307; 507/267; 507/268 |
| Intern'l Class: |
E21B 043/27 |
| Field of Search: |
166/307,300,279
252/8.553
|
References Cited
U.S. Patent Documents
| 4000083 | Dec., 1976 | Heesen | 252/135.
|
| 4001133 | Jan., 1977 | Sorgenfrei et al. | 252/156.
|
| 4017410 | Apr., 1977 | Sorgenfrei et al. | 252/156.
|
| 4451442 | May., 1984 | Jeffrey et al. | 423/224.
|
| 4455287 | Jun., 1984 | Primack et al. | 423/573.
|
| 4574050 | Mar., 1986 | Crowe et al. | 252/8.
|
| 4652435 | Mar., 1987 | Natsuume et al. | 423/265.
|
| 4960527 | Oct., 1990 | Penny | 252/8.
|
| 5114618 | May., 1992 | Gewanter et al. | 252/389.
|
| 5167835 | Dec., 1992 | Harder | 210/750.
|
| 5178796 | Jan., 1993 | Gewanter et al. | 252/389.
|
Other References
Mehltretter, CL, et al, "Sequestration of Sugar Acids" Industrial and
Engineering Chemistry, vol. 45, No. 12, Dec. 1953, pp. 2782-2784.
Williams et al, Acidizing Fundamentals, Chapters 1, 3, 4, 5, 6, 7, 8,
Society of Petroleum Engineers of AIME, New York, 1979.
Smith et al, Secondary Deposition of Iron Compounds Following Acidizing
Treatments, Society of Petroleum Engineers paper No. 2358, presented at
the SPE-AIME Eastern Regional Meeting, Charleston, W.V., Nov. 7-8, 1968.
|
Primary Examiner: Geist; Gary
Attorney, Agent or Firm: Richardson; Peter C., Ginsburg; Paul H., DeBenedictis; Karen
Claims
We claim:
1. A method of preventing the precipitation of an iron (II) salt or iron
(III) salt from an acid or acid solution containing said salt, comprising
dissolving in said acid or acid solution a substance selected from the
group consisting of 2-keto acids, salts of a 2-keto acid, esters of a
2-keto acid, 2,5-diketo acids, salts of a 2,5 diketo acid and esters of a
2,5-diketo acid, wherein said keto and diketo acids, salts and esters are
derived from an aldohexose or an aldopentose.
2. A method of acidizing an oil well comprising forcing into the oil well
formation an acid or acid solution having dissolved in it a substance
selected from the group consisting of 2-keto acids, salts of a 2-keto
acid, esters of a 2-keto acid, 2,5-diketo acids, salts of a 2,5 diketo
acid and esters of a 2,5-diketo acid, wherein said keto and diketo acids,
salts and esters are derived from an aldohexose or an aldopentose.
3. A method of maintaining the dissolution of an iron (II) salt or an iron
(III) salt under oil well acidizing conditions, comprising forcing into an
oil well formation an acid or acid solution having dissolved in it a
substance selected from the group consisting of 2-keto acids, salts of a
2-keto acid, esters of a 2-keto acid, 2,5-diketo acids, salts of a 2,5
diketo acid and esters of a 2,5-diketo acid, wherein said keto and diketo
acids, salts and esters are derived from an aldohexose or an aldopentose.
4. A method of chelating ferric ion which is dissolved in an acid or acid
solution under oil well acidizing conditions, comprising dissolving in
said acid or acid solution prior to forcing said acid or acid solution
into the oil well formation a substance selected from the group consisting
of 2-keto acids, salts of a 2-keto acid, esters of a 2-keto acid,
2,5-diketo acids, salts of a 2,5-diketo acid and esters of a 2,5-diketo
acid, wherein said keto and diketo acids, salts and esters are derived
from an aldohexose or an aldopentose, and then forcing said solution into
said formation.
5. A method of reducing ferric ion which is dissolved in an acid or acid
solution under oil well acidizing conditions, comprising dissolving in
said acid or acid solution prior to forcing said acid or acid solution
into the oil well formation, a substance selected from the group
consisting of 2-keto acids, salts of a 2-keto acid, esters of a 2-keto
acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters of a
2,5-diketo acid, wherein said keto and diketo acids, salts and esters are
derived from an aldohexose or an aldopentose, and then forcing said
solution into said formation.
6. A method according to claim 1, wherein said substance is a compound or
salt having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+ NHR.sup.3 R.sup.4 R.sup.5, wherein R.sup.3, R.sup.4 and R.sup.5
are selected from the group consisting of hydrogen and (C.sub.1 -C.sub.6)
alkyl, and wherein either one or two of the --CHOH-- groups that comprise
the (CHOH).sub.m portion of the compound or salt is replaced by a
##STR2##
group to form, respectively, a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
7. A method according to claim 2, wherein said substance is a compound or
salt having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+NHR.sup.3 R.sup.4 R.sup.5, wherein R.sup.3, R.sup.4 and R.sup.5
are selected from the group consisting of hydrogen and (C.sub.1 -C.sub.6)
alkyl, and wherein either one or two of the --CHOH-- groups that comprise
the (CHOH).sub.m portion of the compound or salt is replaced by a
##STR3##
group to form, respectively, a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
8. A method according to claim 3, wherein said substance is a compound or
salt having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+ NHR.sup.3 R.sup.4 R.sup.5, wherein R.sup.3, R.sup.4 and R.sup.5
are selected from the group consisting of hydrogen and (C.sub.1 -C.sub.6)
alkyl, and wherein either one or two of the --CHOH-- groups that comprise
the (CHOH).sub.m portion of the compound or salt is replaced by a
##STR4##
group to form, respectively, a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
9. A method according to claim 4, wherein said substance is a compound or
salt having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+ NHR.sup.3 R.sup.4 R.sup.5, wherein R.sup.3, R.sup.4 and R.sup.5
are selected from the group consisting of hydrogen and (C.sub.1 -C.sub.6)
alkyl, and wherein either one or two of the --CHOH-- groups that comprise
the (CHOH).sub.m portion of the compound or salt is replaced by a
##STR5##
group to form, respectively, a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
10. A method according to claim 5, wherein said substance is a compound or
salt having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+ NHR.sup.3 R.sup.4 R.sup.5, wherein R.sup.3, R.sup.4 and R.sup.5
are selected from the group consisting of hydrogen and (C.sub.1 -C.sub.6)
alkyl, and wherein either one or two of the --CHOH-- groups that comprise
the (CHOH).sub.m portion of the compound or salt is replaced by a
##STR6##
group to form, respectively, a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
11. A method according to claim 6, wherein said substance is selected from
the group consisting of 2-ketogluconic acid and 2-ketogluconates.
12. A method according to claim 7, wherein said substance is selected from
the group consisting of 2-ketogluconic acid and 2-ketogluconates.
13. A method according to claim 8, wherein said substance is selected from
the group consisting of 2-ketogluconic acid and 2-ketogluconates.
14. A method according to claim 9, wherein said substance is selected from
the group consisting of 2-ketogluconic acid and 2-ketogluconates.
15. A method according to claim 10, wherein said substance is selected from
the group consisting of 2-ketogluconic acid and 2-ketogluconates.
16. A method according to claim 11, wherein said substance is
2-ketogluconic acid.
17. A method according to claim 11, wherein said substance is ammonium
2-ketogluconate.
18. A method according to claim 11, wherein said substance is sodium
2-ketogluconate.
19. A method according to claim 12, wherein said substance is
2-ketogluconic acid.
20. A method according to claim 12, wherein said substance is ammonium
2-ketogluconate.
21. A method according to claim 12, wherein said substance is sodium
2-ketogluconate.
22. A method according to claim 13, wherein said substance is
2-ketogluconic acid.
23. A method according to claim 13, wherein said substance is ammonium
2-ketogluconate.
24. A method according to claim 13, wherein said substance is sodium
2-ketogluconate.
25. A method according to claim 14, wherein said substance is
2-ketogluconic acid.
26. A method according to claim 14, wherein said substance is ammonium
2-ketogluconate.
27. A method according to claim 14, wherein said substance is sodium
2-ketogluconate.
28. A method according to claim 15, wherein said substance is
2-ketogluconic acid.
29. A method according to claim 15, wherein said substance is ammonium
2-ketogluconate.
30. A method according to claim 15, wherein said substance is sodium
2-ketogluconate.
31. A method according to claim 2, wherein the oil well acidizing technique
employed is matrix acidizing.
32. A method according to claim 3, wherein the oil well acidizing technique
employed is matrix acidizing.
33. A method according to claim 4, wherein the oil well acidizing technique
employed is matrix acidizing.
34. A method according to claim 5, wherein the oil well acidizing technique
employed is matrix acidizing.
Description
BACKGROUND OF THE INVENTION
This invention relates to the use of certain keto and diketo acids, esters
and salts that are derived from aldohexoses and aldopentoses, to maintain
very high levels of iron in solution under oil well acidizing conditions.
The compounds described herein chelate ferric iron at low temperatures and
are activated by heat to reduce ferric iron to the more soluble ferrous
species at high temperatures. Because of these properties and their
extraordinarily high solubility in hydrochloric acid, such compounds are
capable of maintaining considerably more iron in solution than competing
materials.
When the formation around oil producing wells become plugged with acid
soluble minerals, the flow of fluid through the oil bearing formation is
reduced and oil production falls. Wells can be stimulated to produce at
higher levels by forcing acid into the formation to dissolve the minerals
that are causing the problem. The acid readily dissolves iron and iron
containing compounds both from the well casing and the formation. As the
acid is neutralized by water and carbonates in the formation, iron will
re-precipitate as ferric hydroxide above a pH of 2.2 unless suitable
chemicals are added to maintain it in a soluble state.
Two approaches have been used to control reprecipitation of iron as acid is
spent and the pH rises, sequestration by organic chelants and reduction to
the more soluble ferrous ion. Commonly used organic chelants include
citric acid, gluconic acid, the tetrasodium salt of
ethylenediaminetetraacetic acid (EDTA), and the trisodium salt of
nitrilotriacetic acid (NTA). Smith, et al., Secondary Deposition of Iron
Compounds Following Acidizing Treatments, paper SPE (Society of Petroleum
Engineers) 2358 presented at the SPE-AIME (American Institute of Mining,
Metallurgical and Petroleum Engineers) Eastern Regional Meeting,
Charleston, W. VA., Nov. 7-8, 1.68), have discussed the relative merits of
each. Gluconic acid is ineffective at elevated temperatures. Citric acid,
is effective only at low temperatures. Also, the formation of insoluble
calcium citrate limits the level at which it can be used. EDTA is
effective at high temperatures and is not prone to precipitation as the
calcium salt. However, it is of limited solubility in hydrochloric and
other acids. NTA is effective without having the negative attributes of
either EDTA or citric acid. NTA, however, has been proven to cause cancers
in laboratory animals. (See Chemical Status Report issued by the National
Toxicology Program, Division of Toxicology Research and Testing, Oct. 8,
1991, p 25.)
While ferric iron will precipitate as the pH rises above 2.2, ferrous iron
remains soluble up to a pH of about 7. Erythorbic acid and sodium
erythorbate have been used commercially to control the concentration of
dissolved iron in acidizing operations by reducing the ferric iron to the
more soluble ferrous species. Crowe et al., in U.S. Pat. No. 4,574,050,
argue that this approach is effective in maintaining substantially more
iron in solution than can be maintained using the above-mentioned
chelating agents.
An ideal additive for controlling the concentration of dissolved iron under
oil well acidizing conditions should have a high solubility in the acid
employed in the acidizing process, prevent precipitation of high levels of
dissolved iron over a wide temperature range, and remain functional for
several hours until the spent acid is pumped out of the formation.
SUMMARY OF THE INVENTION
This invention relates to a method of preventing the precipitation of an
iron (II) salt or iron (III) salt from an acid or acid solution,
comprising dissolving in said acid or acid solution a substance selected
from the group consisting of 2-keto acids, salts of a 2-keto acid, esters
of a 2-keto acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters
of a 2,5-diketo acid, wherein said keto and diketo acids, salts and esters
are derived from an aldohexose or an aldopentose.
This invention also relates to a method of acidizing an oil well,
comprising forcing (e.g. pumping or injecting) into the oil well formation
an acid or acid solution having dissolved in it a substance selected from
the group consisting of 2-keto acids, salts of a 2-keto acid, esters of a
2-keto acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters of a
2,5-diketo acid, wherein said keto and diketo acids, salts and esters are
derived from an aldohexose or an aldopentose.
This invention also relates to a method of maintaining the dissolution of
an iron (II) salt or an iron (III) salt under oil well acidizing
conditions, comprising forcing into an oil well formation an acid or acid
solution having dissolved in it a substance selected from the group
consisting of 2-keto acids, salts of a 2-keto acid, esters of a 2-keto
acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters of a
2,5-diketo acid, wherein said keto and diketo acids, salts and esters are
derived from an aldohexose or an aldopentose.
This invention also relates to a method of chelating ferric iron which is
dissolved in an acid or acid solution under oil well acidizing conditions,
comprising dissolving in said acid or acid solution prior to forcing said
acid or acid solution into the oil well formation a substance selected
from the group consisting of 2-keto acids, salts of a 2-keto acid, esters
of a 2-keto acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters
of a 2,5-diketo acid, wherein said keto and diketo acids, salts and esters
are derived from an aldohexose or an aldopentose.
This invention also relates to a method of reducing ferric iron which is
dissolved in an acid or acid solution under oil well acidizing conditions,
comprising dissolving in said acid or acid solution prior to forcing said
acid or acid solution into the oil well formation a substance selected
from the group consisting of 2-keto acids, salts of a 2-keto acid, esters
of a 2-keto acid, 2,5-diketo acids, salts of a 2,5-diketo acid and esters
of a 2,5-diketo acid, wherein said keto and diketo acids, salts and esters
are derived from an aldohexose or an aldopentose.
A preferred embodiment of this invention relates to a method of acidizing
an oil well, comprising forcing into the oil well formation an acid or
acid solution having dissolved in it a substance selected from the group
consisting of 2-keto acids, salts of a 2-keto acid, esters of a 2-keto
acid, 2,5-diketo acids, of a 2,5-diketo acid and esters of a 2,5-diketo
acid, wherein said keto and diketo acids, salts and esters are derived
from an aldohexose or an aldopentose, and wherein the oil well acidizing
technique employed is matrix acidizing.
Another preferred embodiment of this invention relates to a method of
maintaining the dissolution of an iron (II) salt or an iron (III) salt
under oil well acidizing conditions, comprising forcing into an oil well
formation an acid or acid solution having dissolved in it a substance
selected from the group consisting of 2-keto acids, salts of a 2-keto
acid, esters of a 2-keto acid, 2,5-diketo acids, salts of a 2,5-diketo
acid and esters of a 2,5-diketo acid, wherein said keto and diketo acids,
salts and esters are derived from an aldohexose or an aldopentose, and
wherein the oil well acidizing technique employed is matrix acidizing.
Another preferred embodiment of this invention relates to a method of
reducing ferric iron which is dissolved in an acid or acid solution under
oil well acidizing conditions, comprising dissolving in said acid or acid
solution prior to forcing said acid or acid solution into the oil well
formation a substance selected from the group consisting of 2-keto acids,
salts of a 2-keto acid, esters of a 2-keto acid, 2,5-diketo acids, salts
of a 2,5-diketo acid and esters of a 2,5-diketo acid, wherein said keto
and diketo acids, salts and esters are derived from an aldohexose or an
aldopentose, and wherein the oil well acidizing technique employed is
matrix acidizing.
Another preferred embodiment of this invention relates to a method of
chelating ferric iron which is dissolved in an acid or acid solution under
oil well acidizing conditions, comprising dissolving in said acid or acid
solution prior to forcing said acid or acid solution into the oil well
formation a substance selected from the group consisting of 2-keto acids,
salts of a 2-keto acid, esters of a 2-keto acid, 2,5-diketo acids, salts
of a 2,5-diketo acid and esters of a 2,5-diketo acid, wherein said keto
and diketo acids, salts and esters are derived from an aldohexose or an
aldopentose, and wherein the oil well acidizing technique employed is
matrix acidizing.
Other preferred embodiments of the present invention are those methods
described above wherein the substance utilized is a compound or salt
having the formula CH.sub.2 OH(CHOH).sub.m COOR.sup.1 or (CH.sub.2
OH(CHOH).sub.m COO.sup.-).sub.n R.sup.2, respectively, wherein m is 3 or
4, n is 1 or 2, R.sup.1 is selected from the group consisting of hydrogen
and (C.sub.1 -C.sub.6) alkyl, and R.sup.2 is selected from the group
consisting of the alkali metal cations, the alkaline earth metal cations
and .sup.+ NHR.sup.3 R.sup.4 and R.sup.5 are selected from the group
consisting of hydrogen and (C.sub.1 -C.sub.6) alkyl, and wherein either
one or two of the --CHOH-- group that comprises the (CHOH).sub.m portion
of the compound or salt is replaced by a
##STR1##
group to form, respectively a 2-keto or 2,5-diketo acid, ester or salt,
with the proviso that n is 1 when R.sup.2 is an alkali metal cation or an
ammonium cation and n is 2 when R.sup.2 is an alkaline earth metal cation.
More preferred embodiments of the present invention are the preferred
methods referred to immediately above, wherein the compound or salt that
is dissolved in the acid or acid solution is selected from the group
consisting of 2-ketogluconic acid and 2-ketogluconates. Especially
preferred are the same methods wherein the compound or salt that is
dissolved in the acid or acid solution is sodium 2-ketogluconate, ammonium
2-ketogluconate or 2-ketogluconic acid.
Examples of other embodiments of the present invention are those methods
described above wherein the compound or salt that is dissolved in the acid
or acid solution is 2,5-diketogulonic acid, 2-ketogulonic acid or
2,5-diketogluconic acid.
DETAILED DESCRIPTION OF THE INVENTION
When the formation around oil producing wells become plugged with acid
soluble minerals, the flow of fluid through the oil bearing formation is
reduced and oil production falls. Wells can be stimulated to produce at
higher levels by forcing acid into the formation to dissolve the minerals
that are causing the problem. The acid readily dissolves iron and iron
containing compounds both from the well casing and the formation.
Oil well acidizing is a term well-known to those skilled in the art of
petroleum engineering. It includes such techniques or procedures as "acid
washing", "matrix acidizing" and "acid fracturing", which are also well
known to those skilled in the art. A description of these procedures and
the conditions under which they are carried out is provided by Bert B.
Williams, John L. Gidley and Robert S. Schechter in their book entitled
"Acidizing Fundamentals", published by the Society of Petroleum Engineers
of AIME, New York, 1979, which is incorporated herein by reference in its
entirety.
Several of the preferred embodiments of this invention relate to methods
that utilize a technique known as matrix acidizing. Matrix acidizing
refers to the injection of acid into a formation porosity (intergrannular,
vagular or fracture) at a pressure below that necessary to open a
fracture. (See Williams et al., chap. 2, p. 5.) The purpose of matrix
acidizing is to effect radial penetration of the acid into the formation
to increase the permeability of the formation in a region of reduced
permeability near the wellbore (due to damage) by enlarging pore spaces
and dissolving particles clogging such spaces. (See Williams et al., chap.
2, p. 5.) Because matrix acidizing is done without fracturing the
formation, it is often used to avoid a shale break or other disruption of
a natural flow boundary that could result in the unwanted production of
water or gas.
The specific oil well acidizing conditions employed (e.g., the rate and
pressure of injection and the composition, volume and concentration of the
acid) will vary depending on the temperature of the formation and the
structural characteristics of the well or field (e.g., depth, reservoir
pressure, permeability, and the radii of the wellbore and damage zone or
region). The choice of these conditions in a given situation will be
obvious to those skilled in the art of petroleum engineering. Williams et
al., in chapters 9 and 10 of "Acidizing Fundamentals," referred to above,
describe how to design and carry out appropriate matrix acidizing
procedures for sandstone and carbonate formations, respectively.
The acids and acid solutions contemplated for use in connection with this
invention are those that are generally used in oil well acidizing
procedures. Such acids and acid solutions include hydrochloric acid,
hydrofluoric acid, organic acids formic, acetic and propionic acids, and
mixtures of two or more of the foregoing acids. When aqueous hydrochloric
acid is used, it is generally used in a concentration of about 10% to
about 30%.
The aldopentose and aldohexose derivatives contemplated for use in
connection with this invention are generally used in a concentrations
ranging from about 0.5% by weight of the acid solution in which they are
dissolved to their maximum solubility in such solution.
Most acidizing procedures generally take from about 2 to about 22 hours,
and are conducted at temperatures ranging from about 20.degree. C. to
about 130.degree. C.
As indicated above, as the acid that is utilized in an acidizing procedure
is neutralized by carbonates in the oil well formation, iron will
re-precipitate as ferric hydroxide above a pH of 2.2 unless suitable
chemicals are added to maintain it in a soluble state. An ideal additive
for control of iron under oil well acidizing conditions should have a high
solubility in the acid or acid solution employed in the acidizing process,
prevent precipitation of high levels of dissolved iron over a wide
temperature range, and remain functional for several hours until the spent
acid or acid solution is pumped out of the formation. As illustrated in
Examples 1 to 6 below, the aldohexose and aldopentose derivatives of the
present invention meet all of the these criteria.
The present invention is illustrated by the following examples. It will be
understood, however, that the invention is not limited to the specific
details of these examples.
GENERAL EXPERIMENTAL PROCEDURE
A test solution was prepared by combining iron (as FeCl.sub.3.6H.sub.2 O,
predissolved in 15% HCl) and an additive and diluting to 100 g with 15%
hydrochloric acid. A 1000 ml Erlenmeyer flask containing 70 g granular
dolomitic limestone (42% MgCO.sub.3, minimum assay, 53% CaCO.sub.3,
minimum assay) was immersed in an oil bath set for the test temperature,
and into this flask was poured 100 g of the test solution. To minimize
evaporative losses, the flask was capped with a rubber stopper through
which a syringe needle was inserted to allow for escape of carbon dioxide.
Samples withdrawn at intervals of 1, 2, 3, and 22 hours were passed
through 0.22 micron filters, diluted and analyzed for total iron by atomic
absorption spectroscopy and for ferrous iron by a colorimetric assay using
1,10-phenanthroline.
EXAMPLE 1
To evaluate the relative activity of commonly used iron control agents,
test solutions containing 9.68 g (0.036 mole) FeCl.sub.3.6H.sub.2 O and an
additive in the amount indicated in Table 1 (page 4) were diluted to 100 g
with 15% HCl. Test solutions were treated according to the General
Experimental Procedure described above. For the materials listed in Table
1, the amount of iron remaining in solution after 24 hours at various test
temperatures is shown in Table 2. Erythorbic acid,
ammonium-2-ketogluconate and 2-ketogluconic acid retained virtually the
entire iron charge in solution after 24 hours at all temperatures tested.
The slight increase in iron found in higher temperature experiments is
likely due to slight evaporative losses over the 24 hour test period. The
most effective chelating agents were EDTA and NTA, both of which showed
intermediate activity across the temperature range employed. Iron
chelation by citric acid and sodium gluconate was very good at room
temperature. However, at higher temperature, these materials showed
inferior iron control capabilities relative to the other substances
tested.
TABLE 1
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CHARGE
ABBRE- WEIGHT MOLES
ADDITIVE VIATION (g) CHARGED
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2-Ketogluconic acid
2-ketoacid 6.95 0.036
Ammonium Am-2-keto 7.52 0.036
2-ketogluconate
Ethylenediaminete-
EDTA 13.61 0.036
traacetic acid
tetrasodium salt
Citric acid Citric 6.87 0.036
Nitrilotriacetic acid
NTA 6.84 0.036
Sodium gluconate
Na Glu 7.81 0.036
Erythorbic acid
Ery acid 6.31 0.036
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TABLE 2
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PPM IRON REMAINING IN SOLUTION
AFTER 22 HOURS
Additive .degree.C.
23.degree. C.
50.degree. C.
70.degree. C.
90.degree. C.
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2-Ketoacid 19,300 22,800 23,000
20,900
Am-2-keto 18,700 21,900 21,900
21,300
Ery Acid 20,700 22,900 23,000
24,200
Citric 20,800 12,200 3,600
1,300
EDTA 20,700 18,100 18,300
8,900
NTA 17,300 11,500 15,200
14,000
Na Glu 21,100 0 0 0
Blank 3,300 400 400 300
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The mechanism by which additives listed in Table 1 retain iron in solution
varies with chemical structure and with temperature. Erythorbic acid is
the most powerful reducing agent tested and is effective in reducing all
iron present at room temperature. Citric acid, sodium gluconate, NTA and
EDTA are not reducing agents for iron. Rather, they solubilize ferric iron
by chelation. The 2-ketogluconic acid derivatives solubilize ferric iron
at lower temperatures by chelation and at higher temperatures reduce
ferric ion to ferrous ion. The relative effectiveness of various additives
in reducing ferric iron is indicated in Table 3.
TABLE 3
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PERCENT REDUCTION OF FERRIC
ION TO FERROUS ION AFTER 22 HOURS
ADDITIVE .degree.C.
23.degree. C.
50.degree. C.
70.degree. C.
90.degree. C.
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2-Ketoacid 10.8 75 88 100
Am-2-keto 11.7 81.5 89.2 100
Ery Acid 100 100 98 100
NTA 1.3 0.7 2.2 2.2
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EXAMPLE 2
Iron reduction rate as a function of temperature was determined using the
General Experimental Procedure and ammonium 2-ketogluconate as a
representative example. The results are set forth in Table 4. The results
show that while virtually no reduction occurs at room temperature,
conversion to ferrous is complete within 24 hours at 50.degree. C. At
higher temperatures, the rate is substantially faster, reduction being
complete within 3 hours at 70.degree. C. and within 1 hour at 90.degree.
C.
TABLE 4
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RATE OF REDUCTION OF FERRIC ION BY
AMMONIUM 2-KETOGLUCONATE
PPM FERROUS IRON
TIME .degree.C.
50.degree. C.
70.degree. C.
90.degree. C.
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0 hour 0 0 0
1 hour 935 12,650 23,055
2 hours 1,840 17,665
3 hours 3,335 19,520
4 hours 4,165
5 hours 5,325
6 hours 6,635
22 hours 21,500 20,155 21,530
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EXAMPLE 3
The effect of a molar overcharge on the ability of an additive to control
iron was tested using the same conditions as in Example 1, except that the
amount of additive was doubled. The results are set forth in Table 5. At
24 hours, acidizing solutions containing sodium gluconate and NTA showed
improved iron control at the higher additive level, however, those
prepared using citric did not. EDTA was not soluble beyond the 1:1 molar
ratio and, therefore, not tested at the higher level. In order to test the
limits of 2-ketoglucanates, a greater amount of iron is required.
TABLE 5
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PPM IRON REMAINING IN SOLUTION AFTER 24 HOURS
(MOLAR RATIO ADDITIVE: IRON = 2:1)
ADDITIVE .degree.C.
23.degree. C.
70.degree. C.
90.degree. C.
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2-Ketoacid 20,900 21,800 25,700
Am-2-keto 20,500 19,700 23,500
Na Glu 21,100 16,800 22,100
Citric 21,600 5,800 1,100
NTA 21,700 22,700 18,400
Blank 3,300 400 300
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The following two examples are designed to determine how much iron could be
controlled by a given dose of additive and to approximate the maximum
amount of iron that could be controlled in an acidizing operation by the
most effective additives.
EXAMPLE 4
Dose response profiles for ammonium-2-ketogluconate, erythorbic acid, EDTA,
and NTA (trisodium salt) were determined using the General Experimental
Procedure described above. In each experiment 9.68 g of
FeCl.sub.3.6H.sub.2 O were added per 100 g of test solution to give a
nominal 20,000 ppm Fe in the test solution, which was then spent on
dolomitic lime at 90.degree. C. for 24 hours. The amount of additive was
varied between 2% and 8% on a solids basis. The results, which are set
forth in Table 6, indicate that while not as effective as erythorbic acid,
ammonium 2-ketogluconate is effective at a far lower concentration than
either EDTA or NTA.
TABLE 6
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PPM (X1000) IRON REMAINING
IN SOLUTION AFTER 24 HOURS
AT 90.degree. C.
ADDITIVE CONC. %
ADDITIVE
1.85
2.0 2.77
3.0 3.70
4.0 4.62
5.0 5.55
6.0 6.47
7.0
7.40
8.0
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Am-2-keto 11.5 15.4 23.6 23.9 21.6 20.7 21.5
NA3NTA 2.30 4.20 6.10 10.2 10.4 13.1 14.2
EDTA 2.10 4.20 4.60 7.40 7.20 8.0 10.1
Erythorbic
24.4 24.4 21.6 26.3 21.3 20.3 20.9
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EXAMPLE 5
The amount of iron controlled by some additives is limited by relatively
low solubility in the acidizing media. The exceptional solubility of
2-ketogluconates in hydrochloric acid solutions is shown in Table 7. The
solubility of 2-ketogluconates, coupled with their ability to chelate and
reduce ferric ion, as demonstrated above, renders them capable of
maintaining high levels of iron in solution. To demonstrate this effect,
the solutions described in Table 8 containing 15% and 20% ammonium
2-ketogluconate and 15% and 20% sodium 2-ketogluconate were prepared and
spent on 70 g of dolomitic lime for 22.degree. hours at 90.degree. C.
Analysis of the filtered liquid showed iron present at 56,000 to 58,000
ppm, nearly equivalent to the nominal 60,000 ppm charged to the reaction
flask.
By way of contrast, the highest amount of iron that could be controlled by
NTA was somewhat less than 20,000 ppm and occurred under the conditions
described in Example 3. Attempts to prepare test solutions containing
higher levels of NTA either could not be made up due to limited solubility
or failed to remain soluble over the 22 hour test period.
TABLE 7
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2-KETOGLUCONATE SOLUBILITY AT 23.degree. C.
Conc. HCl Additive
Am-2-keto Na-2-keto
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5% HCl 46.7% 50.8%
10% HCl 53.3% 57.8%
15% HCl 72.5% 54.7%
20% HCl 63.0% 35.2%
25% HCl 30.7% 8.1%
30% HCl 17.2% 4.2%
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TABLE 8
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SOLUBLE FE,
EX- ppm at 22
AMPLE TEST SOLUTION COMPOSITION
HRS
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5a Ammonium-2-ketogluconate
15.0 g 57,400
FeCl.sub.3.6H.sub.2 O
29.1 g
15% HCl 55.9 g
5b Ammonium-2-ketogluconate
20.0 g 57,800
FeCl.sub.3.6H.sub.2 O
29.1 g
15% HCl 50.9 g
5c Sodium-2-ketogluconate
15.0 g 56,200
FeCl.sub.3.6H.sub.2 O
29.1 g
15% HCl 55.9 g
5d Sodium-2-ketogluconate
20.0 g 56,800
FeCl.sub.3.6H.sub.2 O
29.1 g
15% HCl 50.9 g
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EXAMPLE 6
Iron control was shown to be possible with methyl-2-ketogluconate. Using
the experimental procedure described in Example 1 and 7.45 g of
methyl-2-ketogluconate as the additive, samples were removed at 1,2, and 3
hours from flasks incubating at 70.degree. and 90.degree. C. The samples
were filtered and analyzed for both ferrous and total iron. The results
are set forth in Table 9. While the data shows excellent iron control over
the three hour test period, a sludge formed overnight and in neither case
could soluble iron be determined at 22 hours.
TABLE 9
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IRON CONTROL USING METHYL-2-KETOGLUCONATE
Soluble Iron (ppm)
70.degree. C. 90.degree. C.
Time, Hrs. Fe III Fe II Fe III
Fe II
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1 20,700 10,000 22,400
22,100
2 18,800 13,500 21,700
22,100
3 21,900 15,500 22,000
22,100
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